Cartridge fuse



Jan# 19. 1965 F. HOLLMANN ETAL 3,166,656

CARTRIDGE FUSE Filed Jan. 25. 1961 INVENTORSI FRITZ HOLLMANN HANS EMMERICH United States Patent 1 Claim. (ci. 20o-12o) The invention relates to a cartridge fuse, to its construction and a process of manufacturing the same, and, more par-ticularly, to such a manufacture using materials which do not leave solid, electrically conduct-ive residues, as binders for the production of an arc-quenching core of porous structure and of permanent shape.

In our co-pending application-Serial Number 56,722, led September 19, 1960, we have described` a cartridge fuse Iwhose housing is a hollow body, manufactured by casting from a plastic material as a single piece, and a process for its manufacture which is distinguished by the fact that the fusible link and the ends of the associated conductor members, rigidly connected therewith, are imbedded in a mass of arc-quenching substance to which a slight amount of a binder, which does not adversely affect its porosity, has been added. After hardening of the binder, the quenched core thus obtained, permanent in shape, is enveloped, in a correspondingly larger mold, by the material forming the cartridge housing.

Experiences with cartridge fuses made by this process have shown that for the solidiiication of the extinguisher, usually consisting of dry sand, to a shape-retaining but sufficiently porous core not every hardenable or thermosetting binde-r is suitable. This is the case because among the numerous binders used in the casting art, basically suited for the manufacture of sufficiently strong and porous sand cores,-there are those which emit, at theA high temperatures occurring during the melting of the fuses, vapors or gases which retard the extinguishing' of the arc, formed during and on account of the melting of the fuse, to such an extent lthat the cartridge housing explodes owing to the pressure generated. Hence, such binders cannot be considered for the solidiiication of the quencher cores, a requirement for an arc quencher being that the conductive spark gap, created upon the melting ofthe fuse link, be rendered non-conductive as rapidly as possible by the evaporated and condensed quenching ingredients. The known arc quenchers accomplish this in their loose state within the extremely short periody of a few thousandths of a second. This eifect would be eliminated by the binders described above.

When certairpother binders are used which do not emit detrimental gases or vapors, it has been established `that these binders leave behind, after termination of the extinguishing process, small quantities of conductive residues which suffice to form an electrically conductive bridge between the terminals, thereby preventing attainment of the required insulation value of the fuse after melting. These binders, hence, like-wise are unusuable for the purpose at hand.

Therefore, solely those materials can be considered as l3,166,656 Patented Jan. 19, 1965 binders for quencher cores which, upon decomposition by the heat of the arc, neither give rise to gases or vapors ionizing the spark gap, nor leave behind a residue of solid and electrically conductive materials (e.g., carbon black) in quantities suliicient for the for the formation of a current bridge. Examples of unusable binders of the kind described are a number of synthetic resins, for instance, epoxy and phenolic resins.

Pursuant to this invention we propose to use as binders in the manufacture of a shape-retaining, porous quencher core in the production of cartridge fuses such materials which, upon decomposition by the heat of an arc, do not exhibit the drawbacks set forth above.

It has been found that suitable solidifiers or binders for the purpose described vare the following: melamine resins, silicon resins, and calcium sulfate.

A further feature of the invention, therefore, is the employment of melamine resins, silicone resins and calcium sulfate, either singly or in mixtures, as binders in the manufacture of a porous and shape-retaining quencher core.

The invention is illustrated in the accompanying drawing in which FIGS. 1 and 2 are cross-sectional views of a cartridge fuse as described above in two successive stages of manufacturing.

The cartridge fuse shown in the drawing comprises a pair of contact members 1, 2, bridged by a' fuse link having two branches 4, 5. A core 3, composed of an arc-quenching substance of the character set forth, envelops the terminal portions of contact members 1, 2 and the intervening links 4, 5. The vcore 3 is in turn encapsulated in a housing or shell` 6, FIG. 2, consisting of an integrally molded piece of plastic material.

`We claim as our invention:

In a cartridge fuse having a pair of contact members bridged by a fusible link, an arc-quenching core encapsulating said link in intimate contact therewith and a housing enclosing said core, the improvement whereby said core is a solid body which consists of a molded porous mass of sand having admixed therewith a minor proportion of a binder selectedfrom the group which consists of melamine resins, silicone resins, calcium sulfate, and mixtures thereof.

References Cited by the Examiner UNITED STATES PATENTS 11/33 Meissner 18-59 1,947,085 2/34 Hill et al 18-59 2,328,825 9/43 McMahon ZOO-149 2,768,264 10/56 Jones et al 20D-144 2,816,990 12/57 Gelzheiser 200-120 2,830,156 4/ 58 Burgess 200-131 2,866,038 12/58 Kozacka ZOO-120 2,941,905 6/ 60 Hofmann 18-59 2,948,930 8/60 Herbst 18--59 2,949,641 8/60 Quackenbush 18-59 2,961,514 1l/60 Lindell 200-120 3,030,597 4/62 Piaia et al l859 ALEXANDER H. BRODMERKEL, Primary Examiner. WILLIAM I. STEPHENSON, Examiner. 

